Read the entire article HERE on compositesworld.com.

Speed of execution was a concern when developing the manufacturing process, because production volumes for the ZR1 fall between 1,500 and 2,000 units annually, making this the first “mass-produced” all-CFRP hood.
Despite the difficulty of the molding process,  each part can be molded in a single tooling operation (vs. multiple stampings required in metals) owing to the inherent strength and bending stiffness of the CFRP materials. During development, Plasan investigated a variety of different layup, kit and bagging methods to find a process combination that yielded the best appearance and performance within the shortest processing time.

Hood production begins with kit cutting. Rolls of carbon prepreg are loaded onto a cutting table supplied by Eastman Machine (Buffalo, N.Y.) and cut into an individual kit of pieces needed to produce a complete hood (separate sets for outer and inner). Because Plasan is producing a number of CFRP parts for the ZR1, managing and organizing kits is a major aspect of production. Kit components are hand-layed into single-sided, female steel tools produced by Models & Tools (Shelby Township, Mich.). Notwithstanding their complexity and high tolerance control, the tools (one each for top and bottom panels) cost $1 million (USD) less than tools for a comparable SMC hood.  Highly trained layup technicians visually inspect prepregs and use special techniques to position plies precisely on the first try to minimize pulling or stretching of plies, which could distort the appearance, explains Lars Severance, Plasan’s manufacturing engineer.

Shown below: A technician sets up one of Plasan’s two flatbed cutting systems in preparation for kitting the prepreg plies for the hood parts. Source: Plasan Carbon Composites

When layup is complete, the parts are vacuum bagged and moved to one of Plasan’s four production-size autoclaves where, thanks to ACG’s fast-cure epoxy, they cure in about 10 minutes. The total production cycle time for a hood, from layup through cure, is about 60 minutes.

Because of their complex plan-view sweeps, demolded parts are edge-machined on an automated, high-speed, 5-axis robotic router from KMT Robotic Solutions (Auburn Hills, Mich.), which is capable of cutting very tight radii and negotiating complex slope changes at high spindle loads. 

Next, the hood inner and outer panels are prepped for adhesive application and placed in a bonding cell. Here, they are robotically bonded around the perimeter edges using a two-part structural urethane specially formulated by Ashland Inc. (Dublin, Ohio) to cure quickly, survive paint-bake oven temperatures and exhibit the high strength necessary to prevent debonding of inner and outer panels under the stresses of high-speed operating conditions.   

Each hood is 100-percent hand finished. Trained technicians sand the outers and hand-polish the inners to a diamond-like finish, giving it the look of a clearcoat without the expense of the extra step. Then, the inner panel is masked, the assembly is passed through Plasan’s primer booth and, when cured, the primed hoods are shipped to Creative Liquid Coatings (Ft. Wayne, Ind.) to be painted. Just before final quality-control inspection, the polycarbonate window is joined to the hood assembly. To accommodate the coefficient of thermal expansion (CTE) mismatch between the CFRP and the PC, technicians use a special compliant shear/ductile urethane adhesive, also provided by Ashland.  In what has been described as the only real challenge encountered in the window’s development, early installs had a few tiny leaks as the team learned to use the adhesive and equipment, but the problem was soon eliminated.

Completed units are shipped to GM’s Bowling Green, Ky., assembly plant for installation on ZR1s.